Use Camera/Window projection when texture painting?
You can give your model a secondary UV map to base your mask on, using Project from View through your camera you have sized to match your mask image. Call up the mask image in the Masking tab either in the mask tool itself or in the Texture Paint tool, and invert as you need to.
Add your image to the image editor to see the scale and set up your camera to match.

Added a second UV mapping layer

Before painting, showing the original mapping active for target image

Here is the paint on top of the mask, holes showing through